1. Field of the Invention
The present invention relates to an image display apparatus provided with an electron source, and a method for producing the same.
2. Related Background Art
In an apparatus for displaying an image by irradiating a fluorescent member, which is an image displaying member, with an electron beam from an electron source to cause the fluorescent member to emit light, it is necessary to maintain the interior of a vacuum chamber, containing the electron beam and the image displaying member, at a high vacuum. If the pressure in the vacuum chamber is elevated by gas generated therein, such gas detrimentally influences the electron source to lower the amount of electron emission, thereby disabling the display of a bright image, though the level of such influence depends on the kind of the gas. Also, such generated gas is ionized by the electron beam, and the generated ions are accelerated by the electric field and may collide with the electron source, causing damage thereto. A discharge may also be generated in the vacuum chamber, eventually leading to the destruction of the apparatus.
The vacuum chamber of the image display apparatus is usually formed by combining glass members and adhering the joints thereof with, for example, flit glass, and, once the adhesion is completed, the pressure in the vacuum chamber is maintained by a getter provided in the vacuum chamber. In the ordinary cathode ray tube, an alloy principally composed of barium is heated by an electric current or a high frequency radio wave in the vacuum chamber to form an evaporation film therein, and the high vacuum in the vacuum chamber is maintained by absorbing the gas generated therein by such evaporation film.
However, in the recently developed flat panel display utilizing the electron source consisting of a plurality of electron emitting elements provided on a flat substrate, a specific drawback is that the gas generated from the image displaying member reaches the electron source before reaching the getter, thereby inducing a local increase of the pressure and deterioration of the electron source resulting therefrom.
In order to resolve this drawback, in the flat panel image display of a certain structure, there is proposed a configuration of providing a getter in the image display area to immediately absorb the generated gas.
For example, Japanese Patent Application Laid-open No. 4-12436 discloses, in an electron source having a gate electrode for extracting the electron beam, a method of forming such a gate electrode with a getter material, and shows, as an example, an electron source of an electric field emission type utilizing a conical projection as the cathode and a semiconductor electron source having a pn junction. Also, Japanese Patent Application Laid-open No. 63-181248 discloses, in a flat panel display having an electrode (such as a grid) for controlling the electron beam between a group of cathodes and a face plate of the vacuum chamber, a method of forming a film of a getter material of such a controlling electrode.
Also, U.S. Pat. No. 5,453,659 xe2x80x9cAnode plate for flat panel display having integrated getterxe2x80x9d, issued on Sep. 26, 1995 to Wallace et al., discloses a getter member formed in the gap between the striped fluorescent material on the image display member (anode plate). In this example, the getter is electrically isolated from the fluorescent member and the conductive member electrically connected thereto, and is activated by irradiation with the electron from the electron source while applying a suitable potential to the getter.
Also, Japanese Patent Application Laid-open No. 9-82245 discloses formation of the getter member at the side of the metal back or the electron source substrate. It also discloses activating the getter by providing an exclusive heater wiring and activating such heater, or irradiating the getter with the electron beam.
However, in the above-described image display apparatus, although the deterioration of the electron source caused by the gas generated in the vacuum chamber can be prevented to a certain extent by positioning a larger number of getter members in the vacuum chamber, it is difficult to efficiently absorb such generated gas. This difficulty results in the deterioration of the electron source over time or unevenness in the luminance of the displayed image, unless certain particular consideration is given to the positioning of such getter members.
An object of the present invention is to provide an image display apparatus with little deterioration of the electron emitting characteristics of the electron source over time, and a method for producing the same.
Another object of the present invention is to provide an image display apparatus with little change of the luminance over time, and a method for producing the same.
Still another object of the present invention is to provide an image display apparatus with little generation of unevenness in the image display area over time, and a method for producing the same.
The above-mentioned objects can be attained, according to the present invention, by an image display apparatus provided with an external housing composed of members including, in the external housing, a first substrate and a second substrate positioned with a gap therebetween, an electron source provided on the first substrate, and a fluorescent film and an accelerating electrode provided on the second substrate, the apparatus comprising:
a first getter positioned in the image display area in the external housing; and
a second getter insulated from the electron source and the accelerating electrode and so positioned as to surround the first getter.